Oil monitor sensors have been used for determining the degradation of motor oil by measuring the decrease in resistivity of the oil. This has been accomplished by a motor oil assembly comprising a support member having an outer electrode extending from the support member for immersion in oil in the reservoir having perforations spaced axially therealong. An inner electrode is coaxially disposed within and spaced from the outside electrode with electrical insulation spacing the inner electrode within the outer electrode at the distal ends to present a surface in a plane facing the support member. Oil enters through the perforations of the outer electrode and fills the space between the outer and inner electrodes. An electrical circuit is in direct and immediate electrical contact with the electrodes measuring the resistivity of the oil therebetween. Also, a temperature-sensitive sensor is supported by the support member disposed within the inner electrode encapsulated by heat-conducting potting material for sensing the temperature of the oil.
Unless the perforations are specifically spaced and positioned, the assembly will produce a false reading when removed from the oil reservoir. Thus, the oil monitor may be incorrectly calibrated due to the retained oil, and will produce incorrect measurements when reinserted into the oil reservoir. In addition, electrical current will especially flow from the oil to the temperature sensor to produce inaccurate temperature measurements.